1. Field of the Invention
This invention relates to a process for forming an image, and more particularly to a method for obtaining a relief image which comprises imagewise exposing a photo-sensitive image-forming material and subjecting it to peeling development.
2. Brief Description of the Prior Art
Many methods for forming images by development of a photo-sensitive compositions have been suggested which include, for example, developing an exposed photo-sensitive material by heating a thermal-developing method, by using a suitable radiation ray, by treatment with a gas, by an electrostatic treatment, and by the application of pressure.
One typical dry method is the so-called peeling development process utilizing a photo-sensitive image-forming material comprising a support having thereon layer of a photo-sensitive composition and a cover sheet on the photo-sensitive layer in which the adhesion of the photo-sensitive layer to the support and the cover sheet changes upon exposure. After exposure, the cover sheet is peeled from the support leaving the exposed areas of the photo-sensitive layer on the support or the cover sheet and the unexposed area on the other, both being a relief image.
Image formation by peeling development is simpler than ordinary liquid development, which relies upon a large quantity of water or solvent, because it is conducted in the dry state. Furthermore, only the image area of the photo-sensitive image-forming composition layer remains on the support after peeling, the non-image area is removed. As a result stabilization, that is fixing, of the non-image area essential to photo-sensitive materials developed by an ordinary liquid developing method or thermodeveloping method, can be performed simultaneously with the developing operation. Also in the peeling development method, the photo-sensitive composition in the non-image areas is fixed to the peeled sheet as a solid layer and it can be disposed of easily, which is desirable from the environmental standpoint. When the composition contains useful ingredients, they can be completely recovered and easily re-used. Thus, this processing method is advantageous from the viewpoint of saving resources, too.
Since the time a general procedure for image formation by peeling was published in Japanese Patent Publication No. 9663/63, numerous techniques for peeling development have been suggested. These techniques, are classified based their characteristic features, and are briefly described below.
A three-layer structure composed of a support having thereon a photo-sensitive layer containing a photopolymerizable monomer and a cover sheet laminated to the photo-sensitive layer constitutes an important basis of this art. Peeling development of this type of photo-sensitive material is performed based on the fact that polymerization occurs in the exposed area of the material when the material is exposed imagewise, and the adhesion of the photo-sensitive layer to the support and to the cover sheet differs between the exposed and unexposed area. This is described, for example, in Japanese Patent Publication No. 3193/62 (corresponding to U.S. Pat. No. 3,060,024), Japanese Patent Publication No. 22901/68 (corresponding to U.S. Pat. No. 3,353,955), Japanese Patent Application (OPI) No. 7728/72 (corresponding to U.S. Pat. No. 3,770,438), and U.S. Pat. Nos. 3,060,023 and 3,525,615.
U.S. Pat. Nos. 3,627,529, 3,591,377 and 3,607,264 disclose a similar peeling development photo-sensitive materials consisting essentially of support, photo-sensitive layer and transparent cover sheet in which the photo-sensitive composition contains a photocurable polyester (U.S. Pat. No. 3,591,377), a photocurable olefin compound (U.S. Pat. No. 3,607,264) or a photocuring catalyst and a thiol-containing olefin polymer (U.S. Pat. No. 3,627,529).
The methods described above achieve peeling development based on changes in adhesion incident to the photochemical reaction of a photopolymerizable monomer or a photocurable compound. Methods using other photo-sensitive compounds are also known. For example, Japanese Patent Application (OPI) No. 57819/77 discloses a method which relies on a laminate structure composed of a sheet consisting of a support having formed thereon an adhesive composition layer, and a transparent plastic film coated with a photo-sensitive composition comprising a diazonium salt and a binder, wherein the laminate structure is exposed, and then peeled to leave the unexposed area of the photo-sensitive composition layer on the transparent plastic film and the exposed area on the support.
Japanese Patent Application (OPI) No. 3215/78 (U.S. patent application Ser. No. 810,828, filed June 28, 1977) and No. 126220/77 disclose a photo-sensitive material composed of a photo-sensitive composition layer, a support and a thin film layer comprising a metal or chalcogen compound provided between the support and the photo-sensitive layer, and optionally containing a sheet having an adhesive composition layer formed on the photo-sensitive layer. This sheet is developed based on the phenomenon that peeling development after exposure induces selective separation at the interface between the non-sensitive thin film layer and the support.
In the invention disclosed in Japanese Patent Application (OPI) No. 23632/78, a photo-sensitive composition containing a polyhalogen compound and a polymer having a phenol nucleus is used, and by peeling the transparent film-like material adhering to the photo-sensitive composition layer before or after exposure, an image corresponding to the exposed image is obtained on the support.
British Pat. No. 1,319,295 discloses a peeling development method which comprises laminating a heat-softenable polymeric layer and a powder capable of absorbing infrared rays to a support, exposing the resulting material to infrared rays to impart tackiness imagewise to the heat-softenable polymeric layer, and separating the polymeric layer from the support to form an image on the support.
So far, the basic characteristics of known techniques for image formation by peeling development have been described. Heretofore, the basic principle of peeling development has been the difference in adhesion between the photo-sensitive composition layer and the support induced by exposure to light. For example, according to peeling development, a photopolymerizable or photocurable photo-sensitive composition is used, and upon exposure the adhesion of the photochemical composition in the exposed area, decreases or increases from that before exposure, whereby images are formed in the exposed area and the unexposed areas as on different supports. For example, Japanese Patent Publication No. 9663/63 suggests a method for forming an image which have been suggested comprise exposing a photo-sensitive composition in intimate contact with a cover sheet and peeling the cover sheet utilizing the fact that the photo-sensitive adhesive layer has suitable tackiness at room temperature.
On the other hand, Japanese Patent Application (OPI) Nos. 57819/77, 3215/78 (U.S. patent application Ser. No. 810,828, filed June 28, 1977, now abandoned) and 141003/76, for example, disclose a method in which the adhesiveness of the photo-sensitive composition layer itself at room temperature is not essential. In such a method, the adhesiveness required for peeling development is obtained by providing a pressure-sensitive adhesive layer on the peeling sheet used as a cover sheet. In these techniques, an adhesive peeling sheet is adhered intimately to the photo-sensitive composition layer before or after imagewise exposure, and then it is peeled off. Accordingly, there is more latitude in the selection of the characteristics of the photo-sensitive composition than with the aforesaid methods which rely solely on a photo-polymerizable compound and utilize the tackiness of the photo-sensitive composition layer itself at room temperatures.
Some techniques which improve the delineation of the image by heating the image-forming material at the time of peeling have been disclosed. For example, U.S. Pat. No. 3,060,023 discloses a method which comprises using a mixture of a photopolymerizable monomer and a thermoplastic polymer as a photo-sensitive composition layer, and after exposure, bringing the photo-sensitive layer into intimate contact with a receptor sheet at a temperature of at least 40.degree. C. to thereby selectively soften the unexposed area, i.e., the unpolymerized area of the photopolymerizable monomer, and thermally transfer the image to the receptor sheet. That technique utilizes the transfer of the unexposed (unpolymerized) area of the thermoplastic photopolymerizable composition to the receptor sheet under heat, and it enables a large number of copies by bringing the exposed photopolymerizable composition layer into contact with a suitable support to transfer the unexposed area under heat. Since in this method, a transfer image composed of the unpolymerized area is always utilized as the image, when it is desired to utilize the image obtained on the support further for a printing plate or a photoresist, it is necessary to provide an additional step of curing the transferred image by after treatment, such as exposure.
Japanese Patent Application (OPI) No. 39025/76 discloses a method which comprises imagewise exposing a three-layer image-forming material composed of a metal substrate, a layer of a photo-sensitive composition comprising an addition-polymerizable monomer and polyvinyl butyral and a cover sheet, and peeling the exposed material while heating it, thereby to induce cohesive destruction of the unexposed area (i.e., unpolymerized area) of the photo-sensitive layer and to obtain the same positive image as used in imagewise exposure on the metal substrate which image is utilized as a photoresist image.
Thus, there are examples in which heating is performed at the time of peeling. All of these examples use a layer of a photopolymerizable composition, and facilitate the transfer of an image to an image-receiving sheet by increasing the flowability of the unexposed area through heat.
One method for obtaining a transfer image from a photo-sensitive image-forming material containing an azide compound by dry processing is disclosed in German Pat. No. 1,926,658. This method produces an image on a pre-treated image-receiving sheet by thermal transfer. However, only a sublimable ingredient is transferred to the image-receiving sheet and this results in the formation of a visible image, but no relief image is formed.
In contrast, according to the method described in Japanese Patent Application (OPI) No. 57819/77, an adhesive composition layer is provided in intimate contact with the photo-sensitive composition layer composed of a diazonium compound and a binder, and after imagewise exposure, the two elements are peeled from each other to give a relief image corresponding to the exposed image.